This invention relates to filled elastomer compositions comprising an elastomer, such as a natural or synthetic rubber, and a filler.
Most mineral fillers which are commonly available and are suitable for incorporation in elastomer compositions provide only a relatively small improvement in the strength of the elastomer composition in which they are incorporated because of their relatively coarse particle size or because of the weak chemical affinity between the elastomer and the surface of the filler particles, or a combination of these two factors. Currently the most widely used reinforcing filler for elastomers is carbon black which is a very finely-divided material and, on account of the hydrophobic nature of its surface, has a good affinity with elastomers. The presence of carbon black in an elastomer composition gives a good increase in the strength of the elastomer.
A particularly stringent duty for elastomer compositions is in the manufacture of motor vehicle tires. Heretofore, carbon black has been used almost exclusively as a filler in these compositions because of its good reinforcing properties. A rubber compound used for motor vehicle tires must have good tensile strength properties, good tear strength and good resistance to abrasion. It must also not be subject to significant permanent deformation after tension or compression, such permanent deformation generally being known in the art as "permanent set." Permanent set may be measured after subjecting a sample of the rubber compound to tension, in which case it is known as "tension set," or after compression, in which case it is known as "compression set." Carbon black is most commonly prepared by burning oil under controlled conditions and is therefore likely to become increasingly expensive and in short supply. Many attempts have been made to find a satisfactory replacement for carbon black. For example, it has been proposed to use inter alia kaolin clays, usually after treatment with an organosilane, see for example British Patent Specifications Nos. 882,058; 948,163; 1,062,595; 1,272,287 and 1,430,125 and U.S. Pat. No. 3,290,165. Whilst these known organosilane-treated kaolin clays have enhanced reinforcing properties as compared with the untreated materials, they do not constitute a satisfactory replacement for carbon black in many applications. It is an object of the present invention to provide an elastomer composition incorporating a filler having reinforcing properties which are comparable to those of semi-reinfrocing carbon blacks.